Red blood cell substitutes

Soluble polymerized haemoglobin (polyhaemoglobin) is now in a phase III cli nical trials. Patients have received up to 20 units (10 litres) in trauma s urgery and other surgery. Polyhaemoglobin can be stored for more than I yea r. Haemoglobin solutions have no blood group antigen and can be used as a ' universal donor' oxygen carrier. They can also be sterilized. With a circul ation half-life of 24 hours they are undergoing trials for peri-operative u se. For conditions with potential for ischaemia-reperfusion injuries, a new polyhaemoglobin-superoxide dismutase-catalase, which can reduce oxygen rad icals, is being developed. Recombinant human haemoglobin has been tested in clinical trials, and a new type of recombinant human haemoglobin that has low affinity for nitric oxide is being developed for clinical trials. To in crease the circulation time, artificial red blood cells have been prepared with a bilayer lipid membrane (haemoglobin liposomes) or with a biodegradab le polymer membrane-like polylactide (haemoglobin nanocapsules). Synthetic chemicals such as perfluorochemicals are also being developed and tested in clinical trials as red blood cell substitutes.